The operation of conventional electronic equipment is typically accompanied by the generation of radio frequency and/or electromagnetic radiation in the electronic circuitry of the electronic system. If not properly shielded, such radiation can cause considerable interference with unrelated equipment. Accordingly, it is necessary to effectively shield and ground all sources of radio frequency and electromagnetic radiation within the electronic system.
In instances where the radiation-generating equipment is permanently housed in a container, effective shielding may be accomplished easily through proper construction of the enclosure. However, when the equipment housing is provided with a readily openable access panel or door, effective radio frequency interference (RFI) or electromagnetic interference (EMI) shielding presents more of a problem. Many electronic installations such as computer rooms have been made in the past without a full understanding of the effect of partially unshielded enclosures, such as access doors. Thus, manufacturers and users of older electronic equipment have attempted to upgrade the level of RFI/EMI shielding through retrofit installation of shielding devices around these access openings. To this end, it has been known to provide an RFI/EMI shielding device which may be a knitted wire mesh, knitted wire mesh over an elastomeric core, a conductive elastomeric and similar types of shielding devices. Generally, these shielding devices are attached to the housing by rivets, welds, screws, ect. Preferably, a continuous roll-formed strip metal clip, to which a shielding device has been attached, is used.
The clip is designed so that it may be placed over the edge of the door or panel and retained in place by frictional gripping action of the roll-formed clip. The configuration of the shielding device is such that the device attached to the clip, is brought into contact with a fixed surface of the enclosure when the door or panel is closed, effectively sealing off the narrow gap otherwise typically provided between a door or panel and the oppositely facing surface areas of the housing.
For radiation frequencies between 30 megahertz and 3 gigahertz, it is known to utilize conductive mesh materials, supported internally by an elastomeric core or other similar element, in order to provide adequate shielding. In the manufacture of conventional mesh shielded strips, a tubular sleeve of conductive wire is knitted in the form of a continuous tube closely about the exterior of a resilient core. Typically, this operation is performed twice, once to provide a tightly conforming inner mesh, and a second time to provide an outer tubular mesh. Both tubes surround and are supported internally by the resilient core. The thus shielded core is secured to a continuous mounting strip, clip or the like, for mounting upon the housing to be shielded. Typically, this is done by providing sufficient slack in the outer mesh layer to enable a "tail flange" to be formed of the excess material, which can be secured in some form to a mounting means. A similar application in which the knit is wrapped around the core rather than knitted over the core is also known.
While the prior art gaskets described above perform well, they are relatively costly to assemble onto the cabinet. Also, the tightly knit wire mesh necessitates that a high closure force he used to seal the door, and the combination of the tightly knit mesh and the metal clip makes the gasket heavy, which is detrimental in aerospace and other applications where weight is a critical factor.
The present invention provides a novel and greatly improved mesh covered resilient core shielding gasket, which is inexpensive and lightweight and allows a low closure force.